Quite true. Look at perlre for the comments on the "?<!" operator (zero-width negative lookbehind assertion operator).

This will fix merlyn's code (where $file is the text you are parsing):

my $file = shift;
my $inside = 0;
my $oldpos = 0;
while ($file =~ /(?<!\\)(\Q$start\E|\Q$end\E)/g) {
  if ($1 eq $start) {
    if (++$inside == 1) {
      $oldpos = pos($file) - length($start);
    }
  } else {
    if (--$inside == 0) {
      print substr($file, $oldpos, pos($file)-$oldpos);
    }
  }
}
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the (?<!\\)\Q$start\E will match what is in $start but not preceeded by a '\' character.